1. Field of the Invention
This invention relates generally to display drivers and methods for driving a display, and more particularly to a system and method for driving a display where the pixels of the display can be loaded with data and modulated simultaneously. Even more particularly, this invention relates to a system and method for conserving power in a display system.
2. Description of the Background Art
FIG. 1 shows a data loading and modulation diagram 100 showing a prior art method for driving a display with a pixel array. As shown in FIG. 1, data bits are loaded into the pixels of each row of the display while the light source is turned off. Once data has been loaded into the pixels of each row of the display, then the light source is turned on, and the pixels are modulated for an amount of time depending on the significance of the bits that were loaded. FIG. 1 is based on a four-bit, binary-weighted pulse width modulation (PWM) driving scheme.
The pixels of the display are loaded with data and modulated as follows. Between times t0 and t1, a least significant bit (B0) is loaded into the pixels of each row of the display. Note that loading all the B0 bits takes a finite amount of time, which is defined between times t0 and t1. Between times t0 and t1, the light source that illuminates the display is turned off, as indicated by the “Light Source” indicator 102 near the top of the diagram. Once all B0 bits are loaded, then the light source is turned on and the pixels are modulated between times t1 and t2 such that the values of the particular B0 bits are displayed on their respective pixels for a time dependent on the significance of the B0 bits. Then, during times t2 and t3, the light source is turned off, and a next least significant bit (B1) is loaded into the pixels of each row of the display. Once all B1 bits are loaded, then the light source is turned on, and the pixels are modulated between times t3 and t4 for a time dependent on the significance of the B1 bits. Subsequently, a second next least significant bit (B2) is loaded into the pixels of each row of the display between times t4 and t5. Again, the B2 bits are loaded with the light source turned off. Then, once all B2 bits are loaded, the light source is turned on and the pixels are modulated between times t5 and t6 for a time dependent on the significance of the B2 bits. The most significant bits (B3) are then loaded into the pixels of the display between times t6 and t7 with the light source turned off, and once loading is complete, the pixels are modulated between times t7 and t8 for a time that depends on the significance of the B3 bits. Finally, between times t8 and t9, B0 data is loaded for the next frame with the light source turned off, and the load and modulation process repeats itself.
The prior art driving scheme suffers several drawbacks. Most notably, the display is not illuminated during a significant portion of the frame time because the loading and modulation processes are completely separated, and the light source is off during the loading process. Because the modulation time of the display is equal to the difference between the frame time and the total load time for all bits, the images produced by the pixels appear darker when large portions of the frame time are required for loading data. In other words, the light throughput of the display is reduced as the modulation time decreases and the loading time increases. Another disadvantage of the prior art is that many displays require complicated pixel element designs that facilitate the separation of the loading and modulating processes. As a result, the manufacturing costs and design complexity of the display increases. In addition, because many of the prior art pixels require additional components to operate, there is a larger pitch between adjacent pixels in the display.
What is needed, therefore, is a system and method for driving a display that increases light throughput of the display over a frame during which image data is asserted on the display. What is also needed is a system and method that minimizes the circuit complexity of the pixel elements in the pixel array of the display. What is also needed is a system and method that conserves power consumption of the display system.